definitively

Definitively means clearly and surely, leaving no doubt about what's true.

When someone says something definitively, they're making it clear that their words are based on facts or strong evidence. For instance, if a doctor tells you that a certain treatment will work definitively for your illness, that means she's confident that the information is reliable and trustworthy. You might hear a news anchor say that a new law has been passed definitively, which would mean there's no question about its passage. It's also common to see definitive in scientific or academic writing, where researchers might state their findings definitively after thorough investigation and analysis.